HII
I want to perform QST2 or QST3 using gaussian 16 to determine the transition state. I have got several saddle points for reaction with single imaginary frequency. I am trying to get IRC trajectory starting with TS-geometry.
Should I go to run QST2 or QST3 after getting IRC path?. Or QST2 OR QST3 are necessary apart from TS-Berny to classify the transition state. Is the rout line of QST2 input is same as for TS?
Generally, I had no great success with QST2 nor QST3
The best practice to locate a TS is
a) perform a relaxed scan along the reaction coordinate (bond) under study
you could use something like
# opt=modredundant uMN15L/6-31+g(d,p)
Then add the details at the bottom of the file
B 1 2 S 20 0.100000
b) Take the highest energy point from step a and save it as input file for your TS search , then locate the TS using
# opt=(calcfc,ts,noeigen) uMN15L/6-31+g(d,p) freq
noeigen ensures that you will have only one imag freq
Also, take a look at
https://doi.org/10.1039/D3RE00036B
https://doi.org/10.1021/acs.jpca.8b08071
https://doi.org/10.1039/C7CP06082C
https://doi.org/10.1039/C6RA07761G
https://doi.org/10.1021/jp3087122
Good luck
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